In a semiconductor device process, a plasma process is quite often used in order to decompose compounds when carrying out a film deposition process, an etching process, a cleaning process, and the like. When a compound is decomposed by plasma, radicals (free radicals, or atoms or the like with an unpaired electron) are produced. The radicals have relatively high thermal energy and extremely high reactivity, and are less likely to lose their thermal energy even when they hit, for example, an inner wall of a vacuum chamber several times. Therefore, a sealing member such as a packing member or the like in the vacuum chamber may be degraded by the radicals.
There is a gate valve that is provided with plural sealing members on the same surface of a closure element, as an example of a related art gate valve (see Patent Document 1 below). The sealing members include a sealing ring and a support ring that is located inside the sealing ring. When the closure element is closed, a pressing force applied onto the sealing ring from a valve seat is adjusted by the support ring.    Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2002-228043.